As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics as well as the cell structure are important. The feature size of 256 Mb DRAMs and beyond will be on the order of 0.25 micron or less, and conventional dielectrics such as SiO2 and Si3N4 might not be suitable because of small dielectric constants.
Highly integrated memory devices are expected to require a very thin dielectric films for the 3-dimensional capacitors of cylindrically stacked or trench structures. To meet this requirement, the capacitor dielectric film thickness will be below 2.5 nm of SiO2 equivalent thickness.
Insulating inorganic metal oxide materials (such as ferroelectric materials, perovskite-type materials and pentoxides) are commonly referred to as “high k” materials due to their high dielectric constants, which make them attractive as dielectric materials in capacitors, for example for high density DRAMs and non-volatile memories. Using such materials enables the creation of much smaller and simpler capacitor structures for a given stored charge requirement, enabling the packing density dictated by future circuit design. One such known material is barium strontium titanate. For purposes of interpreting this disclosure and the claims that follow, a “perovskite-type material” is defined to be any material substantially having a perovskite-type crystal structure, including perovskite itself (CaTiO3), and other materials. The crystal structure is referred to as “substantially” a perovskite-type crystal structure to indicate that there can be slight distortions of the structure corresponding to a theoretically ideal perovskite crystal structure in many of the materials having perovskite crystal structures, including, for example, perovskite itself.
It would be desired to develop improved methods of incorporating high k materials into capacitor constructions, and it would particularly be desirable to develop improved methods for incorporating perovskite-type materials into capacitor constructions.